Write a method that queries all Accounts and updates each Account record with a revenue tier tag in the Description field based on their AnnualRevenue value.

Apply these tier classifications:

• Revenue >= 100000000 (100M+): Set Description to 'Enterprise Tier'
• Revenue >= 10000000 (10M+): Set Description to 'Mid-Market Tier'
• Revenue >= 1000000 (1M+): Set Description to 'SMB Tier'
• Revenue < 1000000 or null: Set Description to 'Startup Tier'

The method should return the total number of accounts that were updated (as Integer). Use bulk-safe DML operations and do not use DML statements inside loops.

Examples

// Account with AnnualRevenue = 225000000
// Description should be set to 'Enterprise Tier'

// Account with AnnualRevenue = 15000000
// Description should be set to 'Mid-Market Tier'

// Account with AnnualRevenue = 3000000
// Description should be set to 'SMB Tier'

// Account with AnnualRevenue = 890000
// Description should be set to 'Startup Tier'

// Account with AnnualRevenue = null
// Description should be set to 'Startup Tier'